Push-pull steel cables are known as such in the art.
For example, such a steel cable comprises a core and an intermediate layer with zinc coated filaments and an outer layer of filaments coated with a tin-lead alloy. Although having a low friction resistance due to the tin-lead alloy coating on the filaments of the outer layer, such a cable has a number of drawbacks. Apart from the drawback of using two different types of coatings, zinc for the filaments of the core and the intermediate layer and tin-lead for the filaments of the outer layer, there is the major drawback of using lead in one of the coatings, which may cause environmental problems.
Another example is a steel cable consisting only of stainless steel filaments. Such a cable has the advantage of a good resistance against corrosion but has the drawback inherent to stainless steels that the tensile strength is rather limited, which means that thicker and heavier filaments must be used in order to obtain the same breaking load.
Japanese patent application JP-A-02/093113 discloses a push-pull cable with a coating of polybutylene terephtalate (PBT) resin. Also the liner of the casing of the push-pull cable, i.e. the inner coating of the casing, comprises PBT.
Japanese patent application JP-A-52/033944 discloses a control cable with a coating of a PBT graphite wax. The liner of the casing also comprises PBT graphite wax.